Trying to add physics to leather strap on thors hammer
I can't explain how to get the soft-body physics to work, because I myself still don't entire understand soft-body physics.  

However, I can give an alternate way that I know works.

-Instead of using a curve, create a mesh that is just a single edge-loop, no thickness.

-Add cloth physics to it.

-Select the vertices of the area that is inside the hammer handle (going a couple vertices outside the volume of the handle mesh will help avoid collision glitches as well as add to the stiff look), and add them to a vertex group.

-Under the cloth physics, toggle on "Pinning", and select the vertex group you just made.

-In the modifiers tab, you'll see a cloth physics modifier.  After this modifier (that is, below it), add a solidify modifier; increase the thickness as appropriate.

-Add collision physics to the hammer mesh.

-Parent the strap mesh to the hammer mesh.

-I found that cranking up the "Bending" parameter under the cloth physics goes a long way in emulating the stiff, cord-like physics of the real strap in the movies.